The inventor of the present invention has proposed in Japanese patent application No. 190051/1986 a screw pump wherein a rotatable helical screw is provided in an outer cylinder, and the outer cylinder is provided with an axially extending longitudinal groove. A plurality of partitioning plates partitions spaces between the shaft of the helical screw and adjacent blades from each other so that material fed by the screw pump is efficiently fed without clogging of the screw pump with the material to be fed, because the pressurized material being fed which sticks on the helical screw is scraped off the partitioning plates.
The above-mentioned partitioning plates are operated by a cam mechanism. However, the screw pump lacks reliability in operation. Further, the screw pump easily breaks, because excessive force is exerted on the screw pump when the space between adjacent partitioning plates and the shaft of the helical screw becomes clogged with foreign matter such as gravel. Further gravel once caught in the screw pump is difficult to remove. Further once trouble such as clogging occurs, repairs and inspections become difficult. If concrete in the screw pump cures during failure of the screw pump, it becomes impossible to restore the apparatus so they are inevitably scrapped.
Further, holders for holding the partitioning plates in such manner that they can be slidably moved are unstable in their positioning or height. As for the screw pump, the partitioning plates are operated by means of a cam mechanism or a cylinder. However, the operation of the partitioning plates cannot be timed with certainty when feeding material by these means and cannot with certainty achieve the desired positioning of the partitioning plates.